1. Field of the Invention
The present invention relates to a color picture image formation device for developing the latent images formed on a photosensitive body drum in sequence by use of the color toners different in colors, transferring each of said developed toner images once onto a picture image retaining medium and transferring them on a recording paper after all the toner picture images have been formed on the picture image retaining medium.
A color printer, a color facsimile, a color copier, etc. can be enumerated as this type of unit.
As known, an electrophotography recording unit covers a picture image formation process and a recording paper transfer process, and the picture image formation process further consists of an electrostatic latent image formation process, an electrostatic latent image development process, a transfer process and a fixing process.
In the electrostatic latent image formation process, the electrostatic latent image is formed by optically projecting a picture image on a photosensitive body drum or a photosensitive body belt or by providing electric charge on a dielectric drum.
In the electrostatic latent image development process, the electrostatic latent image is developed by electrostatically adhering the toner as a recording medium onto the electrostatic latent image which has been formed in that manner. The toner which has been used in the development is transferred to the recording paper in the transfer process, then the transferred toner is fixed onto the recording paper in the fixing process.
In such a color recording device as expressing many colors with use of color toners, this invention relates to a color recording device which has a plurality of photosensitive body drums, forms the color toner picture images on said drums, then transfers these color toner picture images sequentially onto the intermediate transfer body, and after all the color picture images have been formed on said intermediate transfer body, they are transferred at a time onto the recording paper for the formation of picture image thereon.
2. Description of the Prior Art
The system of color recording device covers the system for transferring the toners sequentially to the intermediate transfer body from a single photosensitive body drum and the system for developing the respective color toners on a plurality of photosensitive body drums and for transferring the toners sequentially on the intermediate transfer body. The present invention relates to the color picture image formation device of latter construction. FIG. 1 and FIG. 2 show prior art color picture image formation devices of the foregoing type.
The prior art color picture image formation device shown in FIG. 1 comprises an image formation module for respective colors, which has image formation sections 1 and 2 each constituted of a precharge device 1c (not shown in the developing section 2), a write section 1d (not shown in the developing section 2), a toner developing section 1e (not shown in the developing section 2), a discharge device 1f (not shown in the developing section 2) and a cleaner 1g (not shown in the developing section 2).
An intermediate transfer body 3 has any of the constructions suitable of being turned or being tensed via a roller (not shown in the figure) for its running, and respective write transfer sections 1b and 2b consist of transfer devices 1a and 2a for transferring a toner image to said intermediate transfer body 3 and also the respective photosensitive drum sections opposite to the intermediate transfer section 3. Numeral 4 denotes a paper side unit for transferring and fixing the toner image on the paper 100 from the intermediate transfer body 3.
In this type of structure, the respective image formation modules 1 and 2 compensate the phase only by a phase differential portion determined by a circumferential speed and the difference between the distance from write sections 1d (2d is not shown in the figure) on respective photosensitive drums for synthetic overlapping to the write transfer sections 1b and 2b and the distance from the write transfer sections 1b and 2b on the respective intermediate transfer bodies 3 to the output transfer section 4a. A color picture image is formed by writing the data for respective colors to be overlapped on the respective write sections 1d (2d is not shown in the figure), developing the image with use of the respective color toners, transferring the image onto the intermediate transfer body 3 and synthesizing the image on this intermediate transfer body 3.
The intermediate transfer body 3 of the device shown in FIG. 1, is a body that is structured by laying out on a drum an endless hoop material made of dielectric sheet describe in Japanese Unexamined Patent Publication (Kokai) No. 61-13263. And, as mentioned above, this device has any of the suitable constructions either for turning said intermediate transfer body 3 itself or for tensing it via a roller (not shown in the figure) for its running.
The color picture image recording device shown in FIG. 2 is equipped with process units P1, P2, P3 and P4 having 4 pieces of photosensitive body drums 7a, 7b, 7c and 7d, respectively, positioned as their centers and an intermediate transfer body drum 12. The process unit P1 includes a charge device 8a, a latent image formation unit 9a, a developing device 10a and a cleaner 11a which are installed around the photosensitive body drum 7a. The other process units P2 through P4 have similar constructions, wherein numerals 8b, 8c and 8d denote the charge devices, 9b, 9c and 9d the latent image formation units, 10b, 10c and 10d the developing devices and 11b, 11c and 11d the cleaners. The developing agents of respectively different colors are contained in the developing devices 10a through 10d of the respective process units. 3 original colors, Y (yellow), M (magenta) and C (cyan), necessary for color recording, are used respectively in the developing devices 10a, 10b and 10c, while the BK (black) is used, for compensating the black, in the developing device 10d.
The recording by the device shown in FIG. 2 is carried out as per the following procedures.
Simultaneously with the recording paper being unrolled on the carrier road in recording the image, the latent images corresponding to the signals of various colors are formed sequentially on the respective photosensitive body drums 7a through 7d. The latent image is formed by charging the surfaces of respective photosensitive body drums 7a through 7d uniformly by use of the corresponding charge devices 8a through 8d and by forming the image by the latent image formation devices 9a through 9d. The latent images are developed by the developing devices 10a through 10d into the formation of toner images of Y, M, C and BK (black) colors. The toner picture images on these photosensitive body drums 7a through 7d are transferred and overlapped sequentially onto the intermediate transfer body drum 12 for the formation of a toner picture image. After the toner picture image has been formed on the intermediate transfer body 12, said image is transferred on to the recording paper 100 by the transfer device 12 and then fixed thereon.
The intermediate transfer body 12 of the device shown in FIG. 2, as described in the Japanese Unexamined Patent Publication (Kokai) No. 63-311273 proposes and is a metallic support body drum around which a low resistance rubber is rolled up, wherein, as it is stated in the above disclosure be transferred nicely by impressing a constant voltage to the metallic support body drum which becomes the base material of this intermediate transfer body and by sequentially changing the voltage applied to the respective picture image processes P1, P2, P3 and P4.
Because the drum body shown in FIG. 1 adopts such a construction as either arranging on the drum an endless hoop material made of dielectric sheet for its turning, or tensing it via a roller for its running, the intermediate transfer body drum has a problem in its strength in addition to the deterioration in an output resulting from the generation of thermal shrinkage, deformation, etc. of a dielectric film. Moreover it is difficult to uniformly maintain, over a long period of time, the contact width and contact pressure in the contact section between the intermediate transfer body drum and the photosensitive drum because the dielectric film alone is used.
Further the device shown in FIG. 2 is not practical because the potentials of the pre-charge device, development bias and photosensitive body drum as the locations for readjusting the conditions require a very fine adjustment although the potentials of respective picture image processes in the intermediate transfer bodies are adjusted in each process.